Fluorescent lamps, especially compact fluorescent lamps of higher wattage, e.g. 26 W or above this wattage, require high starting voltage. This problem arises primarily at amalgam dosed lamps operated at room temperature, but also occurs in the event of pure mercury dosed lamps operated at lower ambient temperature. The high starting voltage causes compatibility issues even in the field of an increasing number of ballasts and applications. The problem is also related to the fact that an increasing number of luminaries have plastic reflectors rather than metallic ones and the plastic reflector cannot serve as a starting aid. It is difficult to meet the starting voltage requirements specified by the standards without sacrificing lumen output, lumen maintenance and lifetime in the wattage range mentioned.
U.S. Pat. No. 4,523,126 describes a starting aid for shaped discharge lamps. The starting aid is a metal band secured to the discharge tube. The starting voltage reduction sharply depends on the location of the starting bands. This feature implies an accurate positioning of the starting bands relative to cathode location. Experiments were conducted in order to prove the effectiveness of the solution described in the above-cited patent when applied at compact fluorescent lamps, but no significant starting voltage reduction could be accomplished. It is believed that the negative result is due to the different lamp geometry and the different filling gas. A further disadvantage of the starting aid according to the cited patent is a loss in light output due to the shielding action of the starting band. Calculating with the preferred width of starting bands, the lumen loss expected is in the range of 2–4 percent. A further drawback is that a conductive part is placed on a touchable portion of the lamp. When the hot cathode hits the wall of the glass tube at the end of the life of the lamp the wall may crack and a current path may be formed to the metallic starting band. The user of the lamp may be exposed to electrical shock.
A similar design is described in U.S. Pat. No. 4,701,667 in which a ring shape starting aid is applied to fluorescent lamps. This starting aid may cause dangerous electric shock and decreases the light output.
Thus there is a particular need to provide a starting aid which reduces the starting voltage of the fluorescent lamp significantly without decreasing the light output of the lamp and ensures safety against electric shock at the end of the life of the lamp.